Scientific Events

Microscopy, by definition, is the science of using a microscope to observe objects that are unseen by the naked eye. However, astronomical objects such as planets, moons and comets or asteroids are easily identifiable in the night sky, yet scientists are increasingly relying on microscopic methods to investigate their composition, structure, and determine their origins. Whether this is via extra-terrestrial exploration with satellites, landers or rovers, or by studying returned astromaterials in the laboratory itself, the use of microscopy within the diverse field of planetary science is quickly becoming the norm. Correlating multiple microscopic and spectroscopic methods within the scanning electron microscope (SEM) when studying meteorites allows us to extend the spectrum from nano or micro-scale imaging at one end, all the way up to the astronomical scale at the other. For example, the Mars Science Laboratory (MSL) rover, Curiosity, landed in Gale Crater; a region that had been heavily investigated using satellite data from previous mission Mars Odyssey. Using similar infrared microscopic methods in the laboratory, we can distinguish the same compositions within Martian meteorites as those directly observed on the Martian surface.Recent studies (e.g. Stephen et al. 2014; King et al. 2018) have combined traditional SEM imaging and analysis (energy-dispersive spectroscopy - EDS, electron-backscatter diffraction – EBSD, wavelength-dispersive spectroscopy – WDS) with micro Fourier transform infrared (μFT-IR) to inform the varied geological histories of meteorite parent bodies, including aqueous alteration on both asteroids and planets. Further studies combine SEM & TEM imaging with other X-ray techniques at varying scales, i.e. X-ray microscopy (XRM) or X-ray tomography (XRT), to help classify new meteorites and examine potential parent bodies throughout the Solar System (MacArthur et al. 2019).Non-destructive, microscopic methods allow for detailed investigation through multiple volumes that would otherwise be inaccessible without damaging the specimens themselves; a crucial consideration when working with limited material from an extra-terrestrial source. Correlating microscopy techniques across instruments, scales and disciplines is perhaps one of the best approaches to studying these astromaterials, and fully unravelling their geological history, as well as their journey to Earth.References:King et al. (2018) Investigating the history of volatiles in the solar system using synchrotron infrared micro-spectroscopy' Infrared Physics and Technology 94, 244-249.MacArthur et al. (2019) Mineralogical constraints on the thermal history of Martian regolith breccia Northwest Africa 8114, Geochimica et Cosmochimica Acta 246, 267-298.Stephen et al. (2014) Mid-IR mapping of Martian meteorites with 8-micron spatial resolution, Meteoritics and Planetary Science, pp A381. [more]

In this talk, the work within the Biomechanics Research Team at the Laboratory for Mechanics of Materials and Nanostructures of Empa on micromechanics of bone will be presented. Fundamental research on the failure mechanisms of bone on the microscale as a function of loading mode will be discussed. Nanostructural characterization is combined with micromechanical experimentation and mechanical modeling to allow identifying structure-property relationships in this complex nanocomposite. Recent technical developments allowing experiments with well defined boundary and environmental conditions in a broad strain rate range are employed to investigate the effect of water on the strain rate dependence of bone on the microscale. Furthermore, direct clinical applications of this fundamental research for assessing bone quality of patients in clinical studies will be discussed. [more]

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Electron microscopy has advanced very significantly in the last two decades. Electron-optical correction of aberrations, which we introduced for the scanning transmission electron microscope (STEM) in 1997, has allowed STEMs to reach sub-Å resolution from 2002 on. It has led to new STEM capabilities, such as atomic-resolution elemental mapping, and determining the type of single atoms by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS). More recently, we have focused on Ultra-High Energy Resolution EELS (UHERE). We have developed a monochromator and a spectrometer that use multipolar optics similar to the optics of aberration correctors, plus several stabilization methods, and we have reached <5 meV energy resolution at 30 keV primary energy. This has opened up a new field: vibrational spectroscopy in the electron microscope. When collecting large-angle scattering events, vibrational spectroscopy can lead to sub-nm spatial resolution, and when collecting small-angle scattering angle events, it can produce EEL spectra with the electron beam positioned tens of nm away from the probed area. The second geometry has led to a powerful new technique: aloof vibrational analysis of materials, which avoids significant radiation damage. Even more recently, we have focused on combining the analytical techniques with in-situ sample treatment. Our progress includes cooling the sample to liquid N₂ temperature in a side-entry holder capable of reaching better than 1 Å resolution. My talk will review these developments, and illustrate them by application examples. [more]

Portevin Le-Chatelier (PLC) effect is a type of plastic instability that results in severe strain localization, reduction in ductility and formation of surface striations during forming operations. Understanding the underlying microscopic mechanism(s) that govern it requires detailed experimental investigations of the relationships between the phenomenon and local microstructural constituents. Most current models of PLC, both phenomenological and theoretical, are based on descriptions of mesoscopic observations and global responses observed in stress-strain curves. More predictive (or physically based) models will require investigations at the microstructural length-scales. In this talk, it will be shown that the gap in understanding of the microscopic origins and macroscopic manifestations of PLC can be bridged by nanoindentation testing. Specifically, it will be shown that by exploiting the high resolution of force and displacement measurements and the site-specific capabilities of the nanoindenter, coupled with complimentary microstructural characterization techniques, we are able to gain new insight into critical aspects of the PLC effect, including its anisotropy, underlying governing mechanisms and associated activation parameters. [more]

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Dislocations in oxides are typically heavily charged and are surrounded by compensating electric charges. As such they are kinetically more stable than chemical dopants. Adepalli et al. termed dislocations a means for “one-dimensional doping” [1]. As they are often introduced by mechanical methods, they may also be termed “mechanical doping” or “self-doping”, as the charges derive from local concentration of the matrix elements. In the literature dislocations have been demonstrated to enhance oxygen conductivity [1] and improve the figure of merit of thermoelectrics by reducing thermal conductivity through phonon scattering by dislocations [2]. Dislocations have been suggested to improve interfacial reaction kinetics and have been theoretically predicted to pin domain walls in ferroelectrics. In Darmstadt we have so far focused on establishing a set of techniques to introduce dislocations into single crystals at room temperature or enhanced temperature and to study (dislocation) creep. Structural investigations have been performed by dark-field X-ray diffraction, rocking curve analysis [3], TEM, NMR and EPR techniques. The first property evaluations have been done with respect to electrical and thermal conductivity and domain wall pinning. All this has to be seen with the perspective of a just developing field, with many opportunities, many obstacles and a lot of exciting uncertainty. Select examples will be provided on dislocation structures, electrical and thermal conductivity in SrTiO₃ and our first attempts on dislocation creep in BaTiO₃. Time provided, I will show 4 slides on the small brother field: “Elastic-deformation tuned conductivity in piezoelectric ZnO." [1] Adepalli, K. K., Kelsch, M., Merkle, R., and Maier, J., "Enhanced ionic conductivity in polycrystalline TiO2 by "one-dimensional doping''," Phys. Chem.Chem. Phys., 16[10] 4942-51 (2014). [2] S. Il Kim, K. H. Lee, H. A. Mun, S. H. Kim, S. W. Hwang, J. W. Roh, D. J. Yang, W. H. Shin, X. S. Li, Y. H. Lee, G. J. Snyder, S. W. Kim, “Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics“, Science, 348, 109-114 (2015). [3] E.A. Patterson, M. Major, W. Donner, K. Durst, K.G. Webber and J. Rödel, „Temperature dependent deformation and dislocation density in SrTiO3 single crystals”, J. Amer. Ceram. Soc., 99, 3411-120 (2016). [more]